Among insulated gate semiconductor devices such as metal-oxide-semiconductor field-effect transistors (MOSFET) and insulated gate bipolar transistors (IGBT), a technology has been disclosed where one semiconductor chip includes a main insulated gate semiconductor device (hereinafter, main device) and a small-size insulated gate semiconductor device for current detection (hereinafter, current detection device) that is separate from the main device and shares a gate and drain terminal with the main device (see, for example, Patent Documents 1, 2, and 3 below). A resistor for current detection is connected with a source terminal of the current detection device so that very small electrical current proportional to the current flowing through the main device is detected by a voltage drop at the resistor. According to the insulated gate semiconductor devices having such a current detection function (hereinafter, a semiconductor device with a current detection function), the current that flows through the current detection device and is proportional to the current flowing through the main device is detected by the resistor, whereby an alarm is set off or a protection circuit is activated when overcurrent flows in the insulated gate semiconductor device.
FIG. 35 is a plan view of a semiconductor device with a current detection function. FIG. 36 is a sectional view along a line A-A′ depicted in FIG. 35. As depicted in these figures, generally, a current sensing electrode 2 of a current detection device 1 is on the same metal layer as a source electrode 5 of the main device and is separate from the source electrode 5. Between the current sensing electrode 2 and the source electrode 5, a resistor 10 for current detection is connected.
A gate insulator (not shown) and a gate electrode 3 of the current detection device 1 are deposited, respectively, on the same layer as a gate insulator (not shown) and a gate electrode 6 of the main device 4. A drift layer 7 and a drain electrode 8 are shared between the current detection device 1 and the main device 4. The gate electrode 3 of the current detection device 1 and the gate electrode 6 of the main device 4 are connected through a gate electric pad 9. In FIG. 36, a body region and a source region are omitted.
FIG. 37 is a sectional view of a conventional semiconductor device with a current detection function. As depicted in FIG. 37, in the conventional planar gate semiconductor device with a current detection function, an impurity density and a diffusion depth of a body region 12 of the main device 4 are substantially equivalent to the impurity density and the diffusion depth of a body region 11 of the current detection device 1, and curvatures of each edge part are also substantially the same. Further, an interval between adjacent body regions 12 of the main device 4 and an interval between adjacent body regions 11 of the current detection device 1 are substantially equivalent.
FIG. 38 is a sectional view of another example of a conventional semiconductor device with a current detection function. As depicted in FIG. 38, in a conventional trench gate semiconductor device with a current detection function, the depth and the width of a trench 14 of the main device 4 is substantially equivalent to the depth and the width of a trench 13 of the current detection device 1. An interval between adjacent trenches 14 of the main device 4 is substantially equivalent to an interval between adjacent trenches 13 of the current detection device 1. Further, the diffusion depth of a body region 12 of the main device 4 is equal to the diffusion depth of a body region 11 of the current detection device 1.
The impurity density of the body region 12 of the main device 4 is equal to an impurity density of the body region 11 of the current detection device 1. If part of the body region 12 and part of the body region 11 each are not connected with the source electrode 5 or are electrically isolated, the ratio of part of the body region 12 contacting the source electrode 5 is substantially equivalent to the ratio of part of the body region 11 contacting the current sensing electrode 2.
For an IGBT device which controls large amounts of power, there is a problem in that when extremely large current flows, the device is destroyed. When high voltage is applied or large current flows, gate voltage becomes unstable causing non-uniform current or current oscillation. For an IGBT having a current detection function, there is a problem in that delay of protection or unstable oscillation is likely to occur because a feedback loop starting from detection of large current up to reduction of the gate voltage is long.
To address these problems, in a trench gate IGBT structure in which a gate electrode is buried in a trench, an electrode having a similar structure to the trench gate electrode is implanted and is electrically connected to an emitter electrode, which is called a dummy trench IGBT structure (see for example Patent Document 4 below). According to the dummy trench IGBT structure, the potential of the implanted electrode is identical to that of the emitter. Consequently, negative charge generated at an ineffective gate electrode (implanted electrode) can be removed and the influence of the negative charge can be prevented. Therefore, the gate voltage becomes stable even when high voltage is applied or large current flows, and non-uniform current or current oscillation is prevented. Thus, the destruction of the device is prevented even when extremely large current flows.
A conventional semiconductor device having a dummy trench structure and a current detection function is explained. FIG. 39 is a cross-sectional view illustrating a structure of the conventional semiconductor device having a dummy trench structure and a current detection function. As depicted in FIG. 39, in the conventional semiconductor device having a dummy trench structure and a current detection function, a main device 4 and a current detection device 1 both have a dummy trench IGBT structure (hereinafter “first dummy trench structure”) 101. In the case of an IGBT, a body region, a drain electrode, and a source electrode are called a base region, a collector electrode, and an emitter electrode, respectively. The current detection device 1 is formed on the same semiconductor substrate as the main device 4. Therefore, the current detection device 1 and the main device 4 share an n-drift layer 7, a p-collector layer 62, and a collector electrode 8.
Both the current detection device 1 and the main device 4 have multiple trenches on a surface opposite to the n-drift layer 7 and the collector electrode 8. In the trenches, trench gate electrodes 73 and 74 and dummy trench electrodes 75 and 76 are formed where gate electrodes 3 and 6, electrodes made of polycrystalline silicone or the like, are implanted with a gate insulating film flanked by the trench and the electrode. The trench gate electrode 73 and 74 are electrically connected to a gate terminal. The dummy trench electrodes 75 and 76 are not connected to the gate terminal. Since the IGBT controls main current at the gate, the dummy trench electrodes 75 and 76 that are not connected to the gate terminal do not contribute to the control.
In regions between the trench gate electrodes 73 and between trench gate electrodes 74, base regions 56 and 12 are formed. On the surface of the base regions 56 and 12, n+ source regions 55 and 58 are selectively formed so that the n+ source regions 55 and 58 touches the trench gate electrodes 73 or 74. Emitter electrodes 2 and 5 touch the base regions 56 and 12 and the n+ source regions 55 and 58, respectively. P-type floating layers 71 and 72 are formed between the trench gate electrode 73 and the dummy trench electrode 75, between the trench gate electrode 74 and the dummy trench electrode 76, between the dummy trench electrodes 75, and between the dummy trench electrodes 76. Since the p-type floating layers 71 and 72 are separate from the electrodes 2 and 5 with interlayer insulating films 57 and 60 therebetween, the p-type floating layers 71 and 72 are electrically isolated from the emitter electrodes 2 and 5.
As depicted in FIG. 39, the trench gate electrodes 73 of the current detection device 1 and the trench gate electrodes 74 of the main device 4 are electrically connected to each other. As a result, the trench gate electrodes 73 and 74 are driven simultaneously. On the other hand, the emitter electrode 2 of the current detection device 1 and the emitter electrode 5 of the main device 4 are separated. Thus, the path of main current of the current detection device 1 and of the main device 4 are different. In addition, although not shown, the dummy trench electrodes 75 and 76 are connected to, for example, the emitter electrodes 2 and 5 or the p-type floating layers 71 and 72 in order to stabilize the potential.
In FIGS. 37 to 39, the size of the main device 4 is approximately equal to the current detection device 1 but actually, the surface area of the current detection device 1 is several tenths smaller than that of the main device 4. Therefore, reflecting the ratio of the surface areas, the current that flows through the current detection device 1 is several percent of that flowing through the main device 4. Detection of the current flowing through the current detection device 1 enables control of the main device 4 even when overcurrent flows through the main device 4.
Patent Document 1: Japanese Laid-Open Patent Application No. H9-293856
Patent Document 2: Japanese Laid-Open Patent Application No. H4-355968
Patent Document 3: Japanese Laid-Open Patent Application No. H6-29539
Patent Document 4: Japanese Laid-Open Patent Application No. 2003-188382